go/types: untyped shifted constants must fit their expected int type

Fixes #22969.

Change-Id: Ie9d1748c36864a81a633f0016594912ac7dfc005
Reviewed-on: https://go-review.googlesource.com/c/144385Reviewed-by: Alan Donovan <adonovan@google.com>

src/go/types/expr.go

@@ -461,7 +461,11 @@ func (check *Checker) updateExprType(x ast.Expr, typ Type, final bool) {
 			check.invalidOp(x.Pos(), "shifted operand %s (type %s) must be integer", x, typ)
 			return
 		}
-	} else if old.val != nil {
+		// Even if we have an integer, if the value is a constant we
+		// still must check that it is representable as the specific
+		// int type requested (was issue #22969). Fall through here.
+	}
+	if old.val != nil {
 		// If x is a constant, it must be representable as a value of typ.
 		c := operand{old.mode, x, old.typ, old.val, 0}
 		check.convertUntyped(&c, typ)

src/go/types/testdata/shifts.src

@@ -354,3 +354,15 @@ func issue21727() {
 	var _ = string(1 << s)
 	var _ = string(1.0 /* ERROR "cannot convert" */ << s)
 }
+
+func issue22969() {
+	var s uint
+	var a []byte
+	_ = a[0xffffffffffffffff /* ERROR "overflows int" */ <<s] // example from issue 22969
+	_ = make([]int, 0xffffffffffffffff /* ERROR "overflows int" */ << s)
+	_ = make([]int, 0, 0xffffffffffffffff /* ERROR "overflows int" */ << s)
+	var _ byte = 0x100 /* ERROR "overflows byte" */ << s
+	var _ int8 = 0xff /* ERROR "overflows int8" */ << s
+	var _ int16 = 0xffff /* ERROR "overflows int16" */ << s
+	var _ int32 = 0x80000000 /* ERROR "overflows int32" */ << s
+}
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